FIG. 10 illustrates a steering device for an automobile having conventional construction. The rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering-gear unit 2, and as the input shaft 3 rotates, a pair of left and right tie rods 4 are pushed and pulled, which applies a steering angle to the front wheels. The steering wheel 1 is supported by and fastened to the rear-end section of a steering shaft 5, and that steering shaft 5 is passed in the axial direction through a cylindrical shaped steering column 6 and supported by the steering column 6 so as to rotate freely. The front-end section of the steering shaft 5 is connected to the rear-end section of an intermediate shaft 8 by way of a universal joint 7, and the front-end-section of the intermediate shaft 8 is connected to the input shaft 3 by way of another universal joint 9. The front-end section of the steering column 6 is connected to and supported by the rear-end section of a housing 10 that houses parts such as a speed reducer of an electric-powered power steering device, measurement devices and the like. An electric motor 11, which is the power source of the electric-powered power steering device, is supported by the housing 10. Unless otherwise noted, the forward-backward direction, the left-right direction (width direction), and the up-down direction respectively mean the forward-backward direction, left-right direction (width direction), and up-down direction of the vehicle.
As disclosed in JP2012086588 (A) and JP2013018472 (A), a tilt mechanism for adjusting the up-down position of the steering wheel 1, and a telescopic mechanism for adjusting the forward-backward position of the steering wheel 1 according to the physique and operating posture of the operator are assembled in the steering device. The tilt mechanism is constructed by the front-end section of the steering column 6 being supported by the vehicle body by way of a tilt pivot shaft 12 that is arranged in the width direction so as to be able to pivotally displace. Held sections 13 are fastened to a portion near the rear end of the middle section of the steering column 6, and the held sections 13 are held between a pair of left and right support-plate sections 16 of a support bracket 15 that is attached to the vehicle body 14. Long tilt-adjustment holes 18 that extend in the up-down direction are formed in portions of the pair of support-plate sections 16 that are aligned with each other. An adjustment rod 17 is passed through the long tilt-adjustment holes 18 of the held sections 13. The up-down position of the steering wheel 1 can be adjusted within the range that the adjustment rod 17 is able to displace inside the long tilt-adjustment holes 18.
The telescopic mechanism is constructed by the steering shaft 5 and steering column 6 that are able to expand and contract. The steering shaft 5 is constructed by combining and fitting together the rear-end section of an inner shaft 19 on the front side and the front-end section of an outer shaft 20 on the rear side with a non-circular fit such as a spline fit so as to be able to transmit torque and be able to displace in the axial direction. The steering column 6 is constructed by combining and fitting together the rear-end section of an inner column 21 on the front side and the front-end section of an outer column 22 on the rear side so as to be able to displace in the forward-backward direction. Long telescopic-adjustment holes 23 that extend in the axial direction of the steering column 6 are formed in the held sections 13. The adjustment rod 17 is also passed through the long telescopic-adjustment holes 23. The forward-backward position of the steering wheel 1 can be adjusted within the range that the adjustment rod 17 is able to displace in the long telescopic-adjustment holes 23.
A pair of pressure sections is provided in portions of both end sections in the axial direction of the adjustment rod 17 that protrude from the outside surfaces of the pair of support-plate sections 16, and an adjustment lever is provided on one end section in the axial direction of the adjustment rod 17. The space between the pair of pressure sections can be expanded or contracted by an expansion/contraction device that operates based on the operation of the adjustment lever.
By tilting the adjustment lever in a specified direction (typically, downward) when adjusting the up-down position or the forward-backward position of the steering wheel 1, the space between the pair of pressure sections is expanded, and the friction force that acts between the inside surfaces of the pair of support-plate sections 16 and the outside surfaces of the held sections 13 decreases. With this friction force in a decreased state, the position of the steering wheel 1 can be adjusted within the range that the adjustment rod 17 is able to displace inside the long tilt-adjustment holes 18 and the long telescopic-adjustment holes 23. By tilting the adjustment lever in a direction opposite the specified direction (typically upward) after adjustment, the space between the pair of pressure sections is contracted, and by the friction force increasing, the steering wheel 1 is maintained at the adjusted position.
The steering device also includes a shock-absorbing mechanism that allows the steering wheel 1 to displace forward in order to lessen the impact load that is applied to the operator when a secondary collision in which the operator's body collides with the steering wheel 1 during a collision accident occurs. This shock-absorbing mechanism is constructed by supporting the support bracket 15 with respect to the vehicle body 14 so as to be able to detach forward due to impact during a secondary collision.
When adjusting the forward-backward position of the steering wheel 1 in the case of a steering device that includes a telescopic mechanism and shock-absorbing mechanism, when the steering wheel 1 is vigorously made to displace to the very front position, and the rear-end sections of the long telescopic-adjustment holes 23 are made to forcibly hit the outer-circumferential surface of the adjustment rod 17, an impact in the same direction of the impact during a secondary collision is applied to the support bracket 15 by way of the adjustment rod 17.
In order to make it possible to further lessen the impact load that is applied to the operator during a secondary collision, reducing the support strength of the support bracket 15 with respect to the vehicle body 14 is thought possible. However, when this support strength is simply reduced and the steering wheel 1 is vigorously made to displace to the front-end position when adjusting the forward-backward position of the steering wheel 1, looseness occurs in the portion where the support bracket 15 is supported with respect to the vehicle body due to the impact that is applied to the support bracket 15, and there is a possibility that the operator will feel uncomfortable when operating the steering wheel 1. Therefore, together with lessening the impact load during a secondary collision, in order to prevent the occurrence of looseness in the support portion of the support bracket 15 when the steering wheel 1 is vigorously displaced to the front-end position when adjusting the forward-backward position of the steering wheel 1, achieving construction of a steering device that is capable of preventing impact going forward being applied to the support bracket 15 is desired.